You could also have all of the Adventures hosted out of a single specific location, but which can take the party out to other centers of culture sometimes, but the Adventurers' home is in the one specific city, and it is where the adventure is to be found...

Perhaps a frontier town, with an untamed wild nearby, perhaps corrupted by Fae magics or an Undead Blight. Outside the frontier are cities that have more resources and experts, and some places to go for additional Adventuring but if they want to do the Cool Stuff of the game, they'll make their way back to that town eventually.